You can get good Sea Salt at the grocery store or health food store. Many people use Redmonds. Just make sure it's good quality. I believe there is a link at the bottom of CZ that discusses salts.
Sea salt is excellent for the health of the mouth. It also finishes cleaning any oily residue after OPing. It also kills bacteria that may be lingering. Remember how Mom's always made their kids gargle with salt water if they had a sore throat? Mom's know best.